Hybrid electric vehicles (HEV) utilize a combination of an internal combustion engine with an electric motor to provide the power needed to propel a vehicle. This arrangement provides improved fuel economy over a vehicle that has only an internal combustion engine. One method of improving the fuel economy in an HEV is to shutdown the engine during times that the engine operates inefficiently, and is not otherwise needed to propel the vehicle. In these situations, the electric motor is used to provide all of the power needed to propel the vehicle. When the driver power demand increases such that the electric motor can no longer provide enough power to meet the demand, or in other cases such as when the battery state of charge (SOC) drops below a certain level, the engine must start quickly and smoothly in a manner that is nearly transparent to the driver.
Vehicle creep can occur in vehicles including an engine and an automatic transmission. A vehicle creeps when the transmission is in forward or reverse gear, and the driver is not pressing the accelerator pedal. The vehicle moves in forward or reverse direction at a low speed. The driver might apply the brake pedal to slow down the creep speed or completely stop the vehicle. For a conventional powertrain, creep might be realized by controlling the engine speed while the torque converter is slipping. For the hybrid powertrain described above, creep can be realized using a different method, which is the subject of this disclosure.